1. Field of the Invention
This invention relates to a method for producing a colored silk filament by making each silkworm larvae secrete the colored silk filament. More specifically, this invention relates to a method for producing a colored silk filament having excellent color fastness to light, washing and the like.
2. Description of the Related Art
As a typical illustrative dyeing method of silk, the following method is known conventionally.
First, a dyestuff is dissolved in a small amount of boiling water and the resulting dyestuff solution is diluted to a weight about 50 times as much as the weight of silk to be dyed. Sodium sulfate is then added, whereby a dyestuff solution is prepared. Placed next in the solution is silk which has been washed with hot water in advance, followed by gradual heating so that the solution boils in about 30 minutes. The solution is allowed to stand for about 30 minutes to achieve complete adhesion of the dyestuff onto the silk. After the complete adhesion of the dyestuff on the silk, the silk is taken out from the solution, followed by washing with water and drying, whereby colored silk is obtained.
Instead of dyeing cocoons after their formation, it has been attempted to obtain a cocoon which has already been dyed at the time of its formation.
As disclosed, for example, in Japanese Patent Publication No. SHO 54-30944, it is also known to coat with a dyestuff solution the spiracles of each grown larva, which is of from the fourth diapause to the fifth instar, several times so that the dyestuff is adsorbed on the silk glands within the larva. The larva is then allowed to secrete a silk filament from the spinneret thereof, whereby a colored cocoon is produced.
Alternatively, it is also known, as disclosed in Japanese Patent Laid-Open No. HEI 3-193904, to produce a colored cocoon by dipping each silkworm larva in a dyestuff solution to have the dyestuff adsorbed on its silk gland through its spiracles and then allowing the larva to secrete a colored silk filament through the spinnerets.
The former dyeing method in which silk is dipped in a dyestuff solution needs many production steps and in addition, a considerable time and labor are necessary for each production step. Moreover, this method requires the dyestuff solution about 50 times as much in weight as the silk to be dyed. Thus, large-scaled facilities and a large amount of the dyestuff are indispensable for this method.
Another drawback of the former method resides in the difficulty in controlling the temperature and time. Without proper control, crocking from the silk may take place. In addition, the color shade varies delicately depending on the ratio of the dyestuff to water, thereby making it extremely difficult to dye silk in a desired shade.
In the latter method, a colored silk filament is produced by coating the spiracles of each silkworm larva with a dyestuff solution or by dipping the larva in the dyestuff solution so that the solution is adsorbed on the silk glands within the larva, and then allowing the larva to secrete a dyed silk filament through its spinneret to obtain a colored cocoon. The colored cocoon so formed is however accompanied with such a drawback that severe crocking occurs not only when the cocoon is boiled but also when the boiled cocoon is treated or processed to obtain a colored filament. There are still disadvantages that the colored silk filament has inferior color fastness to light, washing and the like owing to the use of the dyestuff and about 30% of larvae die while they are dipped repeatedly in the dyestuff solution.